The goals of this R21 exploratory/developmental research project are to establish the validity and reliability of an innovative multi-sensor board device for measuring physical activity type, amount, and associated energy expenditure. These goals will be addressed through a series of laboratory and field experiments in a group of 60 adults. In Specific Aim 1, we will extend our preliminary work by establishing the accuracy of the multi- sensor board for measuring level and graded treadmill walking and running in the laboratory, as well as more common and natural forms of human movement such as walking up/down stairs, riding up/down an elevator, etc., in a field experiment. Accuracy will be established using the recorded activities (labelled "ground-truth") as the standard measures. In Specific Aim 2, we will expand the current capabilities of the multi-sensor board by "training" the device to provide estimates of energy expenditure associated with the measured activities. Accuracy will be established using oxygen consumption as the standard measure. We hypothesize that the multi-sensor board provides valid and reliable measures of physical activity and its associated energy expenditure in adults under free-living conditions. This work is important because physical activity is a significant component of obesity and chronic disease research, prevention, and treatment. The ability to relate physical activity to health depends on its accurate and precise measurement, which we will establish in this study. None of the currently available methods are fully satisfactory, however, because of problems related to cost, convenience, and measurement error. To overcome these limitations, we introduce a new, portable multi- sensor board capable of capturing diverse cues from ongoing activities. The small sensing unit (2.53 sq. in.) has eight different sensing capabilities, including accelerometry, audio, IR/visible light, high-frequency light, barometric pressure, humidity, temperature, and geophysical location, for measuring a number of different human movements. A distinct advantage over other instruments is that we employ "ubiquitous" technology that will enable people to move around and interact with their environment more naturally than they currently are able to do. For example, the unit can be integrated into existing mobile platforms, such as a cellular telephone, that people already have and use on a daily basis. Our longer-term goal is to establish the new state-of-the-art in measuring physical activity and energy expenditure in free-living populations. This research has numerous applications to public health, including weight control, development of personal assistive devices for rehabilitation, and improving national surveillance of physical activity. The purpose of this research is to determine the accuracy of an innovative multi-sensor board for measuring a number of common human physical activities. This work is important to public health because physical activity is an essential component of obesity and health-related research, prevention, and treatment efforts. The long- term goal of this research is to establish the new state-of-the-art in measuring human physical activity and energy expenditure that will have numerous applications to public health, including weight control, development of personal assistive devices for rehabilitation, and improving national surveillance of physical activity levels in the population. [unreadable] [unreadable] [unreadable]